Does stress make you sick? What we know about stress and the immune system

How does stress impact your health? That question has been studied intensely by psychoneuroimmunology researchers for over 30 years. Vaccines, wound healing, and chronic diseases are some of the ways researchers have measured our immune system health. Stress has been shown to impact all three of these things. First, immune responses to vaccines are delayed or substantially weekend in stressed or distressed individuals. Second, stress and depression are risk factors for having longer infections and delayed wound healing. This is thought to be because of the increase in inflammation (specifically, pro-inflammatory cytokine production) caused by negative emotions like anxiety and depression. Counter-intuitively, the immune system is not weakened but instead is seemingly over reacting to a wound, flooding it with immune cells and proteins but making it more difficult for the healing process to work efficiently. Third, chronic stressors can influence biological markers of disease. For example, chronic stress (like being a mother caring for a chronically ill child) can directly cause long-term changes in pro-inflammatory cytokine production. And having increased inflammatory cytokine levels is a risk factor for cardiovascular disease, cancer, and diabetes. Despite these associations, the exact pathways from chronic stress to disease have not yet been worked out. These are examples of some of the findings linking stress to immunity.
But how is stress actually measured you may be asking? A lot of different ways. A “stressed population” might mean a group of people who are going through something really difficult – like caring for a loved one who is terminally ill. Or “stressed population” could mean that these people self-reported having had a large number of stressful life events (eg. history of abuse, near death experience, severe financial strain, etc) in their past. To be an active consumer of science, it’s important to always look at the methodology of a study because often the way one thing is measured (like stress) has big implications for how we interpret the findings. For example, a study showing that would healing is slowed in a sample of caregivers does not mean that we can get out of helping our roommate after she sprained her ankle with the argument "just the mere act of caring for your will weaken my immune system!"